1. Field to which invention relates
The invention relates to a method for the production of laminated glass sheets with thin wires arranged in a thermoplastic intermediate layer, and more particularly for the production of electrically heated laminated glass sheets, in the case of which the wire supplied from a supply bobbin is fixed in the desired position on the thermoplastic intermediate layer.
2. The prior art
Various methods have been proposed for the production of laminated glass sheets with parallel wires laid in the thermoplastic intermediate layer. In accordance with one of these known methods an array of parallel wires, supplied by separate bobbins, are drawn simultaneously through a spacing device, drawn out to the desired length and then lowered together onto the sheets (see German Pat. No. 870,475). In accordance with a further previously proposed method the array of parallel wires is formed by winding a wire on a frame. The wire is fixed on the frame on two supports extending in a direction which is transverse in relation to the direction of the wire coils. Following this the wire coils are severed and the wire array formed is placed with the help of the supports on the sheet (see Swiss Pat. No. 440,574).
These known methods are therefore only suitable for the production of laminated glass sheets with parallel straight wires. They are not suitable for the production of sheets in which the wires are not straight but have, for example a regular undulating shape. Furthermore, in the case of the simultaneous application of a number of wires there is the danger that all wires may not be tensioned equally so that an absolutely straight arrangement of all wires is not ensured. Finally, these previously proposed methods have the disadvantage that they require a comparatively large amount of manual work.
Furthermore, another method of the type mentioned has been previously proposed in which the wire is supplied from a depositing device, constructed in the form of a sliding shoe, and is pressed into the foil (see German Pat. No. 876,874). This method is primarily used for the production of sheets with an undulating shape of the wires and in this case the depositing device is caused to perform periodical transverse movements over the foil. Instead of a single depositing device it is also possible to provide several adjacently placed depositing devices so that several wires can be fixed simultaneously on the foil.
In the case of the deposit of the wire in an undulating shape the undulating shape is directly produced on the foil surface. Since the wire is diverted again and again and at the same time is subject to a certain tension, a satisfactory arrangement or deposit of the wire is only ensured when the wire is sufficiently fixed as it is laid or deposited on the foil. If this is not done, it will be detached from the foil surface again owing to the tension, necessarily present, in the wire. The degree of fixation required can, however, only be ensured when the laying of the wire on the foil is carried out with a moderate speed. Owing to this rigid limits are set as regards increasing the speed of laying.